Patients with postural hypotentsion due to severe baroreceptor dysfunction after previous radiation and/or surgery defined as a) postural hypotension that cannot be corrected with volume repetition to systolic blood pressure greater than 100 mm Hg and absence of orthostatic changes or symptoms; b) postural hypotension that cannot be corrected with volume repletion to systolic blood pressure greater than 120 mm Hg with orthostatic changes and absence of symptoms.